Physico-Chemical Investigation of Multiple Asymmetric Amphiphilic Diblock Copolymer Morphologies in Solution

Abstract

Asymmetric amphiphilic diblock copolymers are able to form self-assembled crewcut aggregates of multiple morphologies in selective solvents. Micelles are formed by the slow addition of a poor solvent, for the core-forming block, to a solution of the copolymer dissolved in a solvent suitable for both polymer segments. The morphology of the aggregates is affected by a number of factors, such as the solvent composition, the block lengths, the presence of additives, and the temperature. Some of the resulting structures are considered to be equilibrium or near-equilibrium morphologies, which can be kinetically frozen using a number of different techniques. The thermodynamics of micelle formation has been investigated, and equations for the standard Gibbs free energy, enthalpy, and entropy have been formulated. Partial phase diagrams have been constructed, giving the morphological phase boundaries. Knowledge of the location of the boundaries has paved the way for the study of the kinetics and mechanisms of the sphere to rod and rod to vesicle transitions. Both processes have two-step mechanisms, with the second step being rate determining in each case.